1. Field of the Invention
This invention relates to a DC-DC converter. More particularly, this invention relates to an insulating DC-DC converter for a distributed power supply which converts electric power from a distributed direct-current power supply into a medium amount of electric power and an interconnected inverter which uses the DC-DC converter.
2. Description of the Related Art
A distributed power supply system which converts electric power from a distributed direct-current power supply, such as a household fuel cell, a photovoltaic power system, or a wind power system, into a medium amount (0.3 KW to 10 KW) of electric power has a power converter, such as an inverter. In the power converter, the input (primary side) is required to be insulated from the system (secondary side). Use of a high-frequency insulating converter in such a power converter would cause the problem of decreasing efficiency as compared with a non-insulating converter.
Furthermore, since such a power supply as a fuel cell inevitably operates more frequently at an output lower than the rating, the subject of increasing not only efficiency in the aforementioned rated output but also efficiency in an operation at a low output less than 50% of the rated output.